The feature is rolling out over the next few days but its arrival may be subject to your corporate administrative process before you see it. Android users will be getting it "soon," according to a Google blog post.
It doesn't sound like you have any control over what's considered "important," though: "These notifications leverage Gmail's machine learning and artificial intelligence capabilities to identify messages you may want to read first."
Automation like this works for some people, but not if you have an eclectic email inbox and your idea of important varies hourly.
It's a setting you turn on in your app, though historically this type of capability usually requires switching to an already categorized view such asor Important First, which Google doesn't specify in its instructions, and which can be a drawback for some people.